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Paramasivan Halasyamani Kevin R. Heier Michael J. Willis Charlotte L. Stern Kenneth R. Poeppelmeier 《无机化学与普通化学杂志》1996,622(3):479-485
Crystals of CuNb(pyz)2OF5 · (pyz)(H2O) ( 1 ) and [Cu(pyz)2.5]+ [NbF6]? · (pyz) ( 2 ) were grown (150°C and autogeneous pressures) from CuO, 1/2(Nb2O5), (HF)x · pyridine, and H2O in excess pyrazine. Light blue single crystals of ( 1 ) are orthorhombic, crystallizing in space group Cccm (No. 66), with a = 14.547(1) Å, b = 16.135(2) Å, c = 13.803(2) Å, and Z = 8. The structure of ( 1 ) contains corner shared [Cu(pyz)4/2F2/2]+, [Cu(pyz)4/2O2/2], and [NbF4O1/2F1/2]?0.5 octahedra. Orange crystals of ( 2 ) are monoclinic, crystallizing in space group C2/c (No. 15), with a = 11.792(8) Å, b = 17.123(3) Å, c = 17.051(5) Å, β = 90.04(4)°, and Z = 8. The structure of ( 2 ) contains puckered rings of corner shared [Cu(pyz)(pyz)3/2]+ tetrahedra and isolated [NbF6]? anions within the rings. 相似文献
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Zhang L Harrison M Heier LA Zimmerman RD Ravdin L Lockshin M Uluğ AM 《Magnetic resonance imaging》2007,25(3):399-405
BACKGROUND AND PURPOSE: Systemic lupus erythematosus (SLE) is an autoimmune disease in which almost all the organs are involved. Neuropsychiatric SLE is of one of the major concerns in the clinical evaluation of this disease. Routine magnetic resonance imaging (MRI) findings are often nonspecific or negative. In this study, we explored the use of diffusion tensor imaging in assisting with the diagnosis of SLE. METHODS: Data from 34 SLE patients (age range, 18-73 years) and 29 age-matched volunteers (age range, 29-64 years) were analyzed. MRI was performed on a 1.5-T clinical MR scanner with a quadrature head coil. The average diffusion constant (D(av)) and diffusion anisotropy maps [fractional anisotropy (FA)] were determined on a pixel-by-pixel basis. Regional diffusion measurements were made by region of interest in the genu and splenium of the corpus callosum (CC), anterior and posterior limb of the internal capsule (IC) and frontal lobe and thalamus. The diffusion distribution was fitted to a triple-Gaussian model. The mean of the brain tissue distribution was determined as a mean diffusion constant for the whole brain (BD(av)). Student's t test was used to determine the diffusion difference between SLE patients and control subjects. The SLE patients were separated into two groups according to their MRI results. A P value lower than .05 was considered to be statistically significant. RESULTS: Twenty of the 34 SLE patients with abnormal MRI results showed findings dominated by nonspecific white matter disease. The BD(av) and D(av) values of the frontal lobe, splenium CC and anterior IC were significantly higher in all SLE patients as compared with the control subjects. The SLE patients with normal MRI results also showed higher BD(av) and D(av) values in the frontal lobe, splenium and anterior and posterior limbs of the IC as compared with the control subjects. There was no significant difference in the D(av) values of the thalamus between the SLE patients and the control subjects. The BD(av) value in the SLE patient group was robustly correlated with the D(av) values of the frontal lobe, splenium and thalamus. These correlations were found to be similarly significant for the SLE patients with normal MRI findings. The diffusion anisotropy measurements showed that splenium CC had the highest FA value in both the control subjects and SLE patients. Overall, SLE patients had lower FA values in the genu and splenium CC as compared with the control subjects. In the group of patients with normal MRI findings, the FA values of the genu and splenium CC as well as the anterior IC were also lower than those in the control subjects. Pearson's correlation statistics revealed robust correlations between the measurements of D(av) and FA values in the SLE patient group. CONCLUSION: Quantitative diffusion imaging and diffusion anisotropy showed early changes in the brains of the SLE patients. Increased BD(av) and D(av) values of the frontal lobe as well as decreased anisotropy in the genu CC and anterior IC may represent preclinical signs of central nervous system involvement of SLE even when the routine MRI findings are negative or nonspecific. Quantitative diffusion analysis may prove to be useful in detecting the initial brain involvement of SLE and may enable monitoring of early disease progression and treatment efficacy. 相似文献
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R. Mateva KR. Zhilkova G. Zamfirova R. Díaz‐Calleja A. Garcia‐Bernabé 《Journal of Polymer Science.Polymer Physics》2010,48(23):2518-2529
The molecular dynamics of new poly (ω‐dodecalactam‐co‐ε‐caprolactam‐co‐propylene oxide) copolymers (DL/CL/PAC) has been investigated by using dynamic mechanical thermal analysis (DMTA) and dielectric relaxation spectroscopy (DRS) measurements. The copolymers were synthesized via anionic polymerization of relevant lactams activated with carbamoyl derivatives of telechelic hydroxyl terminated polypropylene oxide with isophorone diisocyanate (PAC). The calorimetric, X‐ray diffraction, and DMTA measurements were performed to recognize the influence of the composition ratio and the type of PAC on the physical, thermal, and mechanical properties of the synthesized copolymers. The DRS was used to study the frequency dependence of the dielectric permittivity of some isotherms from ?110 to 145 °C. Copolymerization of ε‐caprolactam with about 10 wt % ω‐dodecalactam results in a copolymer that has lower water absorption, a melting point close to that of polyamide 6 and has a high enough degree of crystallinity in respect to high storage modulus. Five dielectric relaxations have been observed in the dielectric spectra, three at lower temperature and two at higher temperature. The copolymers have two glass transition temperatures for polyamide segments and polyether blocks, indicating microphase separation in the copolymers. Other studies directed toward molecular dynamics of polyamide DL/CL/PAC copolymers have not been reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
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We investigate a wetting reversal transition in thin films of two-phase mixtures of poly(ethylene-propylene) (PEP) and its deuterated analogue (dPEP) on a substrate covered by a self-assembled monolayer (SAM) whose surface energy, γSAM, is tuned by varying the SAM composition. As γSAM increases from 21 to 24 mJ/m2, a transition from a three-layer (air/dPEP/PEP/dPEP/SAM) to a two-layer (air/dPEP/PEP/SAM) structure occurs at increasing Tc - T, where Tc and T are the critical and transition temperatures, respectively. As the system structure changes from three-layer to two-layer, the thicknesses of the dPEP-rich wetting layers at the air/mixture and mixture/SAM interfaces are found to smoothly increase and decrease, respectively, while the thickness of the PEP-rich layer (ca. one half of the total film thickness) does not change. The dependence of the transition temperature on γSAM is predicted by a simple model using the experimental data on the surface energies of PEP/dPEP and estimates of the interfacial energy between PEP and dPEP. 相似文献
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Norquist AJ Heier KR Halasyamani PS Stern CL Poeppelmeier KR 《Inorganic chemistry》2001,40(9):2015-2019
Crystalline KTiOPO4 (KTP), an inorganic nonlinear optical material with a waveguide figure-of-merit that is twice that of other mixed-metal oxides, contains helical chains of TiO(4/2)O(2/2) octahedra in which a long, short Ti-O bond motif results in a net c-directed polarization. The alternating long and short Ti-O bonds that occur along these chains are the major contributors to the large nonlinear optic and electrooptic coefficients. Analogous chains have been constructed using dichromate [Cr2O7]2- anions and [M(py)4]2+ (M = Cu, Zn) cations; these new transition metal oxides crystallize in the same space group as KTP. Crystal data for Cu(py)4Cr2O7: orthorhombic, space group Pna2(1) (No. 33), with a = 15.941(7) A, b = 16.324(3) A, c = 8.857(2) A, and Z = 4; for Zn(py)4Cr2O7, orthorhombic, space group Pna2(1) (No. 33), with a = 16.503(1) A, b = 16.005(1) A, c = 8.8130(5) A, and Z = 4; for Cd(py)4Cr2O7, monoclinic, space group C2/c (No. 15), with a = 14.8034(9) A, b = 11.1847(7) A, c = 15.788(1) A, beta = 110.023(1) degrees, and Z = 4. 相似文献
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Toth R Heier J Tisserant JN Anna EE Braun A Graule T 《Journal of colloid and interface science》2012,378(1):201-209
Dewetting induced self-organisation was used to prepare an ordered microstructure from a highly volatile liquid. Dewetting of an evaporating iron oxide precursor solute on silicon substrate resulted in arrays of microdots with nearly hexagonal and tetragonal symmetries. Ordered structures form either by stick-slip motion or fingering instability at the receding contact line of evaporating droplets. Subsequent thermal treatment at 550 °C yields crystalline Fe(2)O(3) microdots with a diameter range of 1-4 μm. The size, density and shape of the microdots can be changed by using patterned substrates with different surface energies. 相似文献
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